This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The goal of this research is to understand how the cerebellum transforms incoming eye movement signals into the signals that it sends to the oculomotor system. We propose that saccade accuracy depends on a signal that stops saccades at the right time. Initially we thought that this signal traveled across the midline of the cerebellum in the axons called parallel fibers (p-fibers). In the past year we have tested this proposal by cutting these fibers while minimizing damage to the tissue around the cut. We found that cutting p-fibers that cross the midline does not disrupt saccade deceleration. We now believe that a deficit in saccade deceleration resulted from tissue damage around the incision. Currently we are preparing to test this hypothesis by making narrow sagittal lesions along the midline of the cerebellar cortex. In a related experiment we will use anatomical tracing to describe the connections from lateral and medial parts of the cerebellar cortex to determine how different parts of the cerebellum connect to the cerebellar nuclei. Preliminary data show that the lateral and medial areas of the saccade part of the cerebellum make different connections. Describing this will tell us how the cerebellum makes movements of different sizes. In addition to showing how the cerebellum produces signals that make eye movements accurate this work will also show why saccades, and consequently vision, are badly impaired by surgery that damages the cerebellum. This surgery is common because the most common brain tumors in children are immediately under the cerebellum. Thus, our work will motivate and guide easy-to-implement modifications of treatment and surgery to removes tumors without impairing vision. Such improvements could help patients quickly because they require no other innovations.